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H. ZIEBOLZ CONTROL SYSTEM Dec. W49

2 SheiS-Sh6et 1 Filed DeC. 1'7, 1945 INVENTOR! flrberizwogg,

BY m/ M H. ZIEBOLZ CONTROL SYSTEM Dec. 6, 1949 2 Sheets-Sheet 2 Filed Dec. 17, 1945 INVEJf/TOR. /ereri 21/315053, am/fia MM,

Patented Dec. 6, 1949 CONTROL SYSTEM Herbert Ziebolz, Chicago, 111., assignor to Askania Regulator Company, Chicago, 111., a. corporation of Illinois Application December 17. 1945, Serial No. 635,563

15 Claims.

The invention relates generally to asystem for controlling a variable condition, such as pressure, temperature, rate of flow, or the like. and particularly to a system for controlling such conditions under circumstances wherein the condition is rendered highly unstable due to employment of inherently unstable devices in the production of the condition.

Devices that are inherently unstable. for example, blowers and certain types of electric motors, usually have a generally parabolic per-' formance curve. Hence it is readily seen that for any ordinate value there are two abscissa values and unless proper provision is made the device jumps in operation from one abscissa value to the other. It becomes necessary, therefore, in controlling the condition produced by the device to maintain the device operating on one half of its performance curve, usually the half having the larger abscissa values. The extent to which the device may be adjusted thus is limited and an auxiliary means must be employed to aid in the control of the condition.

It is an object of this invention to provide. for an apparatus having an unstable primary device acting as a supply source influencing a condition to be controlled, a new and improved control system which assures proper control of the condition without hunting and yet is simple in construction and direct in operation.

Another object is to provide a control system employing an auxiliary means in addition to regulation of the primary condition generating or influencing device which precludes the primary device from operating on other than the proper portion of its performance curve.

Still another object is to provide a control system regulating a condition by control of a primary condition generating device and an auxiliary means in which the primary device and the auxiliary means are regulated in series in response to the condition to be controlled.

A further object is to provide a control system regulating a condition by control of a primary condition generating device and an auxiliary means in which the primary device and the auxiliary means are regulated in series in response to the condition to be controlled, the primary device being at all times regulated to operate above a certain minimum necessary to prevent shift to operation on the other slope of the performance curve.

Yet a further object is to provide a. control system regulating a condition by a control of a primary condition generating device and an auxiliary means in which the auxiliary means comes into play only when the primary device is reduced to a permissible minimum of operation.

Other and more detailed objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of a control system embodying the features of this invention.

Fig. 2 is a graph illustrating operation of a turbine blower.

Fig. 3 is an enlarged showing of one of the elements of Fig. l.

Fig. 4 is a diagrammatic view illustrating a modified construction of a portion of the signal generating means of Fig. 1.

Fig. 5 is a diagrammatic view illustrating a modified form of control system.

While the invention is susceptible of various modifications and alternative constructions, it is shown in the drawings and will hereinafter be described in a basic embodiment and one modi fication. It is not intended, however, that the invention is to be limited thereby to the specific constructions disclosed. On the contrary, it is in-.- tended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims.

Though the invention is adaptable for the control of a reat variety of conditions, it is for exemplary purposes herein shown and will hereinafter be described as adapted to the control of air pressure in a line supplied by a turbine blower. A turbine blower has been selected because it is typical of various other apparatus that has an unstable operating characteristic making the problem of control thereof a particularly difficult one. Devices such as a turbine blower, certain types of electric motors, etc.. have a generally parabolic operating characteristic with the result that there are two values of one particular operating factor that will satisfy a single value of some other operating factor. In a turbine blower, for

' example, if blower pressure is plotted against flow at diiferent constant speeds of the blower, there will result a series of generally parabolic curves, such as M, n2, 123 and 114 (see Fig. 2), in which as the flow increases the pressure increasesfor a while and thereafter decreases. It will thus be seen that for a given pressure all, for example, there will be two flows ql and Q2 producing that desired pressure. Thus should the pressure in the line being supplied-by the blower exceed the blower pressure for the flow 112. for example, the flow would be reduced and while there might temporarily be an increase in blower pressure (see 113 of Fig. 2) if that increase were not suflicient to overcome the line pressure, the flow would be further reduced and actually reversed, thus going from the value a2 to the value qi and beyond. Such reverse flow would, of course, eventually reduce the pressure in the line and the flow would again jump to the higher flow value corresponding to the pressure pl or any other pressure that might then be present in the line. It is to avoid this pumping operation of the blower that the control system herein disclosed has been designed.

Speaking generally, the condition to be controlled herein is air pressure in a line L. Influencing the condition to be controlled, namely, the air pressure, is a primary device, in this embodiment serving as a source and taking the form of a turbine blower B driven by a motor M. Also utilized to influence and control the condition to be controlled is an auxiliary means herein taking the form of aby-pass or bleeder i3 controlled by a valve ll of appropriate character. In this embodiment, control of the condition is primarily exercised by regulation of the operation of the primary device or blower B with secondary control being exercised by regulation of the by-pass l3. To that end, the control system proper comprises generally a master means, more particularly, a master signal generating means I 5, which is responsive to pressure in the line L and is operable to generate a signal which'is a function of the pressure in the line L. Responsive to this signal is a control means for a means governing the operation of the primary device, that is, the blower B.

While operation of the blower B, that is, flow of air therethrough, might be controlled either by regulation of the speed of the blower or by throttling, the governing means herein takes the latter form and thus comprises any suitable valve, such as a butterfly valve ll, disposed in an intake It! to the blower B. Under these conditions, the blower is, of course, driven at a constant speed by the motor M. The control means and the governing means for the blower just described respond only to a certain portion or range of the signal generated by the signal generating means l5 and serve as a minimum flow regulator maintaining the flow of air from the blower on the high side of the maximum pressure generated by the blower at any given speed. Responsive to a signal calling for a reduction in flow below the minimum flow permissible is a means governing the auxiliary means, namely, the by-pass l3 through the valve H. The means controlling the blower and the means controlling the auxiliary means, namely, the valve II, can thus be said to operate in series in so far as response to the signal is concerned with the means controlling the valve I I responding to a certain range or portion of the signal and with the means controlling the valve l4 responding to a dliferent portion or range of the signal.

Turning now to a more detailed description of the control system, the signal generating means ii (in Fig. 1) includes a jet pipe regulator of the Askania Jet pipe type. Such a regulator comprises a pressure responsive device l6 which is connected by a conduit I! to the line L and has a manually adjustable spring I8 for loading so as to adjust the regulator for maintaining any desired pipe line pressure. Pivotally mounted in well known manner and adaptedto be actuated by the pressure responsive device it is a Jet pipe II from which fluid is elected under pressure against a pair of orifices 23. The orifices 2B are by suitable conduits connected to opposite ends of a cylinder 2| having a piston 22 reciprocable therein and connected to a rod 23 of considerable length. Carried by the rod is a cam 24 engaged by a follower 2! bearing against one end of a compression spring 26, the other end of which bears against the jet pipe IS. The cam 24 and spring 23 function in well known manner to vary the compression of the spring 26 in such manner as to oflset the change in pressure to which the device I! is'subjected and thus restore the jet pipe I! to its neutral position when a signal which is a definite function of the change in pressure in the line L has been generated.

Herein the signal takes the form of linear movement with an increase in pressure in the line L producing downward movement of the rod 28, as viewed in Pig. 1. This signal or movement will hereinafter be known as the reducing" signal, while opposite movement will be known as the increasing" signal. To the end that such movement may be translated into control of the valves II and it, there is carried by the rod 23 a second cam 21 and an end abutment 28. The cam 21, as best seen in Fig. 3, has a cam surface S which is divided into two portions, ranges, or the like SI and S2. The range or portion SI extends obliquely to the axis of the rod 23, widening progressively in the direction of a reducing signal 'or movement, that is, downwardly, as herein arranged, while the portion S2 extends parallel with the axis of the rod 23.

Means is provided herein to actuate or control the primary device governing means, that is, the valve Ii. This means again includes a regulator of the Askania jet type and comprise a pivoted jet pipe 3| discharging fluid impinging against a pair of orifices 32 connected by conduits 33 to opposite ends 01 a cylinder 34. Reciprocable in the cylinder 34 is a piston 35 connected by a linkage 38 of appropriate character to the butterfly valve ll. Bearing at one side against the jet pipe 3! is a compression spring 31 disposed at right angles to the direction of movement of the cam 21 and carrying a cam follower 38 bearing against the cam surface S. Completing the regulator is a pressure responsive device 39 acting on the jet pipe 3| in opposition to the spring 31 and serving to measure the volume of air flow through the blower B by measuring the pressure diiferential across an orifice It positioned in the intake III. The pressure responsive device 39', of course, functions in well "known manner to restore the jet pipe 3| to neutral position when, as a result of adjustment of the valve II, the flow of air through the blower has been increased or decreased in accordance with the signal. It will be understood that the means just described functions to close the valve tain portion or range of the signal. If now the Thus the means con-' trolling the valve II is responsive only to a cersystem is adjusted to maintain minimum flow through the blower at the point of intersection between the two signal ranges, then the valve II and its associated control means will always maintain the flow of air through the blower at of the blower. With varying speeds of the blower B the minimum flow would be represented by a curved line F (Fig. 2). Where, as here, the blower is driven at a constant speed the minimum flow will be determined with relation to that particular speed and will have a constant value represented by the line Q3.

Coming into operation when the signal falls in the portion or range S2 is a means for governing the auxiliary'means exercising control over the condition, namely, the valve N. This governing means comprises a regulator of the Askania jet type comprising a pivoted jet pipe 45 discharging fluid against a single orifice 46 communicating by means of a conduit 41 with one end of a cylinder 48. Reciprocable-in the cylinder is a piston 49=connected by a suitable linkage 50 to the valve 14 and having a compression spring urging the same in opposition to the fluid in the cylinder 48. Interposed in the conduit 41 is a pressure responsive device 52 acting on the jet pipe 45 in opposition to a compression spring 53. The spring 53 is interposed in the path of the rod 23 and is contacted by the end 28 of the rod simultaneously with the reaching of the intersection between the surfaces Si and S2 of the cam 21 by the follower 38. Continued movement of the rod 23 downwardly, as viewed in Fig. 1, places the spring 53 under progressively greater compression and the regulator is herein arranged to produce greater and greater pressure in the conduit 41 as aresult of such compression of the spring 53. This in turn actuates the piston 43 which is here so connected with the valve It as to open the same progressively as the piston is actuated by fluid pressure in the cylinder 48.

Having described the mechanism, the operation thereof will now be briefly described. For this purpose assume that the pressure in the line L is substantially at the value desired to be maintained. At that pressure the signal generating means l5 will have its rod 23 so positioned that the follower 38 will be riding approximately midway of the surface SI, and the end 28 will not be compressing the spring 53 at all or only so lightly as not to cause generation of a pressure sufiicient to overcome spring 5!. Under these circumstances the valve M will be completely closed and there will be no flow of air through the by-pass i 3, while valve l i will be intermediate its full open position and the partially closed position which it may assume and still assure that the volume of air being delivered by the blower is not below the minimum that may be delivered and still keep the operation of the generate a signal of a predetermined character calling for a reduction in the air being supplied to the line L. This signal herein, of course, is in the form of linear movement of the rod 23 and the parts carried thereby, and this movement herein is downward, as. viewed in Fig. -1. Asa

} air.

l result of such longitudinal downward movement of the cam 21 with the rod 23, the follower 3| riding on the surface SI of the cam 21 moves laterally inwardly oi the direction ofcam movement, reducing the compression of the spring 31, producing an unbalance between the spring 31 and the pressure device 33 with resultant pivot- .ing of the jet 3| in a clockwise direction. With such pivoting a pressure-unbalance is caused on the piston 35, actuating the same to adjust the valve ll closer to its minimum open position. This, of course. reduces the flow of air through the intake I6 and thus reduces the pressure differential across the orifice 40, thereby restoring balance between the pressure device 39 and the spring 31, and the jet 3| is again positioned in its neutral position. This change in signal has not been sufllcient to bring the samein the range or portion S2 and there is thus no material change in so far as. the valve I4 is concerned, and this valve thus remains closed. The blower B thus simply discharges a smaller volume of Should further reduction in the consumption of air or some other factor continue to cause the pressure in the line L to rise above the value desired, the operations just described will be continued until the rod 23 has been advanced to such extent that the follower 38 rides at the juncture between the surfaces SI and S2 of the cam 21. Should the pressure continue to rise, the signal generated by the means i5 may be said to take on a different character or to fall in a different portion or range, namely, one in which themean controlling the valve I4 is now responsive to the signal, while the means controlling the valve H is no longer responsive. In terms of the particular construction disclosed in Fig. 1, this means that the follower 38 has now reached the juncture point of the surfaces of cam 21 and further downward movement of the cam 21- merely causes the follower 38 to ride on the surface S2 without change in lateral position. This a rod 23, however, now compresses the spring 53 which would result in unstable operation of the thereby pivoting the jet pipe 45 and causing it to create a larger pressure in the conduit 41. This pressure is now sufilcient to overcome the spring 5| moving the piston 49 upwardly and opening partially the valve I4. By by-passing a portion of the air the pressure'in the-line L is thus reduced without reducing further the output of the blower blower.

Should the pressure in the line L drop due to increased load or some other factor, the operation described would be reversed with the rod 23 of the signal generating means now moved upwardly by-pass had been completely or substantially line L.

aeoons'e mined minmium, and ceasing to be responsive to below that minimum.

In Fi 4 there is disclosed an alternative form or signal generating means II. This means comprises a pressure responsive device I! adapted to be connected by means oi a conduit i'l' to the Influenced by the pressure responsive device It is pivoted jet pipe ll opposingly infiuenced by a compression spring I5 interposed conduit ll with one end of a cylinder II, and

" the other of which is by a short conduit ll connected to one end of a small cylinder ll. The remaining end of the cylinder ii is by a conduit 82 connected to the remaining end of the cylinder I9. Cylinder I! has a piston ll therein, while the cylinder 8| has a piston l4 therein and a piston rod 85 projectin through both ends or the cylinder. Enga ing one end of the rod Ii between the jet pipe l9 and a stationary abutinent 56. The jet pipe I8 is part 01' an Askania Jet type regulator and operates in well known manner to discharge a jet of fluid against a pair of orifices one of which is by a conduit I! connected to one end of a cyiinder'i'l' and the other of which is by a conduit 58 connected to one end of a cylinder 59. The other end of the cylinder 59 is by a conduit 60 connected to the remaining end of the cylinder 2|. Reciprocable in the cylinder 2| is a piston 22' having a rod 23' projecting through one end of the cylinder and carrying a cam 21'. Reciprocable in the cylinder 59 is a piston 6i having a bleed passage therearound so as to permit gradual restoration of the piston to a normal position by a spring 62. This stabilizer piston and cylinder is more fully disclosed and claimed in U. 8. Letters Patent No. 1,959,889. Secured to the piston ii and projecting through one end of the cylinder 59 is a piston rod 63 pivotally connected at one end to a beam 64 fulcrumed at 66 and connected at the other end to the diaphragm of the pressure responsi've device It through the medium of a spring 66.

In Fig. 5 there is disclosed a modified form of control circuit for governing a condition, herein for maintaining substantially constant the air pressure in a conduit L. As in the basic form, primary control over the air pressure is exercised by a blower B which supplies the air to the line L' with the output of the blower controlled by throtting of the intake conduit [0' by means of a butterfly .valve ll as.distinguished from control of the speed of the blower, the blower being driven at a constant speed by motor M. Auxiliary control over the pressure in the line L is exercised by means of a by-pass i3 governed by a valve H of suitable construction. The valves II? and H are still serially responsive to a signal generated by a signal generating means IS". The signal generated by the means i5" has different ranges or portions to which the actuating means for the valves II' and H are respectively responsive, with the means controlling the valve I I again acting as a minimum flow regulator preventing the blower from operating on the unstable portion of its operating curve. The signal generated, however, takes the form of pressure instead of linear movement and thus particularly adapts itself and is advantageous over the form disclosed in Fig. 1 for the control of a plurality of blowers connected to supply the same load.

The signal generating means l5" comprises a regulator 10 of the Askania Jet type including a pressure responsive device H connected by means of a conduit 12 with the line L. The pressure responsive device ll bears at one end against a lever 13 fulerumed at 14 and engaged at its remaining end by a tension spring 15. Transmitting rocking of the lever 13 to a pivoted jet pipe 16 is a linkage mechanism 11. The jet pipe 18 discharges oil in well known manner against a pair of orifices one of which is connected by a is a spring 88 serving yieldably to retain the cylinder 84 in an intermediate or neutral position.

Gradual restoration of the cylinder to neutral position by the spring after dispacement oi the cylinder is permitted by the bleed passage I! connecting opposite ends of the cylinder 8!. The remaining end of the rod 05 is connected to a lever 08 fulcrumed at 89 and bearing at its opposite end against a compression spring II which at its other end bears against the Jet pipe II in opposition to the spring 15.

Secured to the piston 83 and Y projecting through one end of the cylinder II is a piston rod 0| suitably connected to a valve I: to control the same in accordance with the demands or the regulator ill. The valve 02 is an element of a second means or portion or the signal generating means and under the control of the regulator 10 generates a signal in the form of pressure which bears a definite relationship to the change in pressure in the line L. This second means comprises a pump P driven by a motor 03 discharging fluid to a conduit N which in turn discharges to atmosphere through a restricting, fixed orifice II. The volume oi fiuid supplied to the portion of the conduit N intermediate the valve l2 and the orifice II is. of course, determined by the valve 82 and by such variation the pressure 01' the fiuid in that portion or the conduit will also be varied and determined. It is the pressure of the fiuid in this portion of the conduit II that constitutes the signal being generated. The regulator 10 and the valve 9! controlled thereby are so arranged that an increase in pressure in the line L results in a decrease in the pressure signal generated,

while a decrease in pressure in the line L results in the generation of a signal having correspondingly increased pressure values. Connected to the conduit 04 intermediate the valve 02 and the fixed orifice ii is a conduit 0! which thus carries the master signal or master pressure for the control of any number of pressure responsive means governing any number 0! blowers B or auxiliary control means, such as the by-pass i3.

Herein the control means for but a single blower and by-pass are shown in detail. butit will be readily understood how a second, third, etc. similar control means, represented by the broken line rectangles II and III, could be connected to the conduit IS and similarly governed by the master signal or master pressure. Leading from the conduit 98 is a conduit .1 having branches 9! and I. The first oi the branches leads to the pressure responsive device I III of a regulator, generally designated III. This regulator is again of the Askania .Iet type having a pivoted jet I02. The jet II! is influenced by the pressure device Ill through the medium 01' a linkage system I03 which includes a plurality of springs I and I Ila. More specifically, the linkage system comprises a beam Ilia pivoted intermediate its ends on a fulcrum "3b and having one end lltc terminating opposite the pressure responsive device MI to be engaged and rotated in a counterclockwise direction, as vlewed in Fig. 5, when the pressure on the device I rises above a predetermined and critical value. Acting on the opposite end of the beam l03a and tending to urge the beam in a clockwise direction is the compression spring lMa. Rotation of the beam 103a in either direction is preferably limited by stops E0311. Transmitting counterclockwise movement of the beam iota to the pivoted jet pipe N12 is a right angle member We pivoted at the intersection of its arms of a fulcrum 33f. Herein the horizontal arm is positioned for contact by the end I630 of the beam while the vertical arm through a link Hg is connected to the jet m2. The spring EM is an adjustable spring, is connected at one end to the link 13g and serves to maintain minimum flow of air through the blower as will presently become more apparent.

Completing the regulator i0! is a double chambered, pressure responsive device "95 which measures the volume of air being delivered by the blower B by measuring the pressure diiierential across an orifice mt disposed in the intake Ill. The device Hi acts on thejet pipe m in opposition to the spring ltd, so as to maintain a oertain minimum flow of air through the blower, and also acts in opposition to the device 408, when the pressure on that device is high enough to render it effective, so as to restore the jet pipe 32 to neutral position when proper adjustment in the flow of air through the blower has been made. the regulator mi may facilitate understanding. The predetermined and critical value of the master pressure is, of course, that value where there is a change in responsiveness by the primary and the auxiliary control means. At any value of the master pressure above this critical value, the regulator llli will be substantially in the position shown in Fig. 5, assuming that an equilibrium condition exists. With any rise in pressure of the master signal, the jet 802 will be temporarily displaced from its neutral position until restored by adjustment of the flow through the blower. With the value of the master pressure or signal dropping below the critical value,

the spring lMa will overcome the device 590 and will rotate the beam its in a clockwise direction until arrested by abutment with the lower one of the stops mm. The influence of the device Hi0 thus will be entirely removed and control will be entirely under the spring H14 which, as previously stated, has been adjusted to maintain through cooperation with the device Hi5 the minimum permissible flow of air through the blower. v

Controlled by the regulator to actuate the valve 1 l in accordance with the signal is a piston and cylinder device having a cylinder it! and a piston its reciprocable therein and connected through suitable linkage 509 with the valve ll. Opposite ends of the cylinder Ill! are by conduits H0 connected to orifices Iii against which the jet from the jet pipe Hi2 impinges in well known manner.

It is believed apparent from the foregoing that the means governing the blower is responsive to the signal only when it is in its upper range and that, as the master pressure or signal increases in value, the valve U will be opened wider and wider to increase the output of the blower, and that, as the master signal or pressure decreases,

A brief statement of the operation of the valve II will be progressively closed to decrease the output of the blower. At a certain point, however, further reduction in the master signal has no further eiiect on the means governing the blower. This point is so selected that the output of the blower is still above that volume which assures operation of the blower on the stable portion of its operating curve.

Branch 99 leads to a pressure responsive device I [5 which functions as the control means for the by-pass valve M. The valve i4 is through the medium of a spring H8 biased to open position, with the force of the spring and the force of the device H5 being so adjusted that the device H5 overcomes the spring and maintains the valve 84' closed so long as the master pressure or signal is at or above that value to which the regulator ii is responsive. when the master signal or pressure drops below that critical or common value, the pring H6 overcomes the device M5 to progressively greater extents and accordingly opens the valve M and the by-pass l3 controlled thereby to a progressively greater extent. The means for controlling the valve M thus can be said to respond only to the lower portion or range of the master signal and thus the means for governing the blower and the means for governing the by-pass are serially responsive to the signal.

Having described the mechanism, the operation thereof will be briefly described. For this purpose, assume that the pressure in the line L is substantially the pressure desired. This pressure acting through the pressure device H of the regulator ill and through the second means of the signal generating means sets up a master signal or pressure which probably will fall, and herein at least is assumed to fall, in that range of pressures to which the regulator "ii is responsive. If now, due to drop in consumption of air or for some other reason, the pressure in the line L rises, that increase in pressure will cause the signal generating means l5" to produce a correspondingly smaller master signal or pressure. This reduced master signal will through the regulator H3! and actuating means I01, E08 cause the valve i l to be adjusted in a direction reducing the output of the blower. With continued rise in the pres-sure in the line L, the operation just described will be continued until the master pressure or signal reaches that minimum value to which the regulator B85 is responsive. Further reduction in the master signal, due to continued high pressure in the line L, will then have no further eiiect on the regulator EM and the valve M will remain in such partially open position as will assure operation of the blower at such volume as to keep it operating on the stable portion of its performance curve. The signal'now is in its lower range to which the device H5 is responsive and the spring 1 I 6 will open the valve 54' to permit icy-passing of the air and thus serves to reduce, the pressure in the line L.

If now it be assumed that the pressure in the line L drops, the operation and particularly the sequence in which the valves it and H will be actuated will be reversed. Initially the valve 14', unless already in closed position, will be closed for, as the pressure in the line L' drops, the master signal or pressure increases and thus will progressively overcome the spring l is until the valve i4 is completely closed. Should such closing of the by-pass be insumcient to bring the pressure in the line L back to the desired value, the means controlling the valve II will now come into operation and will open the valve ll pro- 11 gressively as the master pressure or signal rises.

It is believed apparent that this form of control circuit, like the circuit disclosed in Fig. 1, functions in a novel manner to control a condition and assures proper control even though influencing the condition thereby controlled is a primary device having an inherently unstable performance curve. This satisfactory operation is assured at all times and under all conditions and is not dependent upon chance balancing of the various control factors nor upon a fortunate time rate of responsiveness of the various control means or elements.

I claim as my invention:

1. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising signal generating means, including a device responsive only to the condition to be controlled,

operable to generate a signal which is a function of the condition, means governing operation of the primary device, means responsive to the control signal and to the rate of operation of the primary device to actuate said primary device governing means, said last named means being actively responsive to the signal only when the signal is in a certain portion of its range, auxiliary means exercising control over the condition and governing means for said auxiliary means responsive only 'to the control signal and actively responsive only when the signal is in a portion of its range different from the first named range.

2. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising signal generating means, including a device responsive only to the condition to be controlled and means controlled by said last named device for translating change in the condition into a signal which is a function of the condition, means governing operation of the primary device, means for actuating said governing means including means responsive to the control signal and means responsive to the operation of the primary device. said governing means actuating means being operable to maintain a certain minimum operation of the primary device, auxiliary means exercising control over the condition, and governing means for said auxiliary means responsive only to the control signal and only when the primary device is near its certain minimum operation.

3. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising signal generating means, including a device responsive only to the condition to be controlled, and means controlled only by said last named device for translating change in the condition into movement of an element, a cam carried by said element, means governing operation of the primary device, means for actuating said governing means including a follower engaging said cam and means responsive to the operation 01' the primary device, said cam being efiective to cause change in the operation of the primary device fer a portion only of the movement of said element. auxiliary means exercising control over the condition, and governing means for said auxiliary means actuated by said element after predetermined movement of said element in a direction calling for reduction in the condition to be controlled.

4. A control system for use wth an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising signal generating means including a device responsive to the condition to be controlled, means under the sole influence of said last named device generating a signal in the form of movement of an element and a cam carried by said element also operable to influence said last mentioned means and cause said last mentioned means to translate change in the condition into movement of said element which is a function of the condition, means governing operation of the primary device, a second cam carried by said element, means for actuating said governing means including a follower engaging said second cam and means responsive to the operation of the primary device, said second cam being effective to cause change of the primary device in proportion to movement of said element but for a portion only of such movement of said element, auxiliary means exercising control over the condition, and governing means for said auxiliary means actuated by said element after predetermined movement of said element in a direction calling for reduction in the condition to be controlled.

5. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising signal generating means including a device responsive to the condition to be controlled and means controlled by said last named device for translating change in the condition into a signal in the form of linear movement of an element which is a function of the condition, the element having an advancing movement when calling for a reduction in the condition and a retracting movement when calling for an increase in the condition, a cam carried by said element having a cam surface with a first portion extending generally parallel with the direction 01' movement of said element and a second portion extending progressively laterally of the path of said element considered in the advancing direction of said element, means governing operation of the primary device, means for actuating said governing means including a follower engaging said cam and mounted for movement laterally of the path or movement of said element and means responsive to the operation of the primary device, auxiliary means exercising control over the condition, and governing means for said auxiliary means actuated by said element after said cam follower leaves said second cam surface and rides on the first cam surface.

6. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising means responsive to the condition to be controlled, means under the control or said last named means for generating a signal in the form of pressure varying as a function of the condition to be controlled, means including pressure responsive means for controlling the operation of the primary device, said last named means responding to a portion only of the signal and be- 76 responding to a portion or the signal diil'erent 13 from the portion responded to by said primary device control means and taking over control of the condition to be controlled when the primary device is at its certain minimum operation.

7. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising means responsive to the condition to be controlled, means under the control of said last named means for generating a signal in the form of pressure varying as a function of the condition to be controlled, means for controlling the operation of the primary device, means for governing said last named means including pres sure means responsive to the signal and counteracting means responsive to the operation of the primary device, said governing means responding to a portion only of the signal and maintaining operation of the primary device above a certain minimum, and auxiliary means exercising control over the condition to be controlled including pressure responsive means responding to a portion of the signal different from the portion responded to by said primary device control means and taking over control of the condition to be controlled when the primary device is at its certain minimum operation.

8. A control system for use with an apparatus having a variable condition which is to be cntrolled and a primary device in the nature of a supply source influencing the condition comprising means for generating a signal which is a function of change in the condition to be con trolled comprising a regulator of the pivoted jet pipe type including a pivoted jet pipe, means responsive to the condition to be controlled acting to displace said jet pipe from neutral position upon change in the condition and means operable as a result of displacement of said jet pipe to restore said jet pipe to neutral position, said last mentioned means including a bleed passage for gradually removing the restoring infiuence of said last mentioned means and pressure generating means controlled by said regula=- tor to generate a master signal pressure, means governing the operation of the primary device, a regulator for controlling the primary device governing means including means responsive to the master signal pressure and means responsive to,

the operation of the primary device, and an auxiliary means exercising control over the condition to be controlled including means responsive to the master signal pressure, the last mentioned means and the pressure responsive means of said last mentioned regulator responding actively to different ranges of pressures of the master signal with said last named regulator ceasing to respond actively while the primary device is still operating above a certain minimum rate.

9. A control system for use with an apparatus having a variable condition which is to be controlled and a primary device in the nature of a supply source influencing the condition comprising means for generating a signal which is a function of change in the condition to be controlled comprising a regulator of the pivoted jet pipe type including a pivoted jet pipe, means responsive to the condition to be controlled acting to displace said jet pipe from neutral position upon change in the condition and means oper-.

- accuses of said last mentioned means and pressure generating means controlled by said regulator to generate a master signal pressure increasing with rise in the condition to be controlled and decreasing with fall in the condition to be controlled, means governing the operation of the primary device, means controlling said primary device governing means biased to maintain a cer-- tain minimum operation of the primary device and including means responsive to the master signal pressure when in its upper range, auxiliary means exercising control over the condition to be controlled biased to tend to reduce the'condition, and means responsive to the master signal pressure operable to hold said auxiliary means inefiective so long as the master signal pressure is in the range to which the pressure responsive means of said primary device controlling means is responsive.

10. A system for controlling pressure in a line supplied from a blower driven at a constant speed comprising signal generating means including a device responsive to the pressure in the line op,- erable to generate a signal which is a function of the pressure in the line, auxiliary means exercising control over the pressure in the line, and a plurality of means each responsive to the signal and respectively governing the blower and the auxiliary means to operate in sequence and independent-1y of other means to control the pressure in the line.

11. A system for controlling pressure in a line supplied from a blower driven at a constant speed comprising signal generating means including a device responsive to the pressure in the line operable to generate a signal which is a function of the pressure in the line, means governing the outable as a result of displacement of said jet pipe to restore said jet pipe to neutral position, said last mentioned means including a bleed passage for gradually removing the restoring influence put of the blower, means'controlling said blower governing means including means responsive to a portion of the signal, auxiliary means exercising control over the pressure in the line, and control means for said auxiliary means responsive to a different portion of the signal, the signal responsive means functioning in sequence, and with the blower control means maintaining a minimum output of the blower.

12. A system for controlling pressure in a line supplied from a blower driven at a constant speed comprising signal generating means including a device-responsive to the pressure in the line operable to generate a signal which is a function of the pressure in the line, a single means for governing the operation of the blower, a regulator for controlling said blower governing means including means responsive to a portion of the signal and means responsive to the rate of operation of the blower, said regulator being onerable to maintain a certain minimum operation of the blower, by-pass means connected to the line, and means controlling said by-pass means including means responsive to the signal and operable to come into play only when said regulator has reduced the blower to minimum' element and a second cam surface extending obliquely to the direction of movement of said element, means for governing the operation of the blower, a regulator for controlling said blower governing means including a cam follower engaging said cam and means responsive to flow of air through the blower acting in opposition to the cam follower, a by-pass connected to the line having a valve controlling the same biased to closed position, and pressure generating means controlled by said element and coming into operation when the cam follower is at the juncture of the cam surfaces to generate a pressure operable progressively to overcome the bias on said by-pass valve and to open'said valve as said element continues its movement in a direction calling for further reduction in the pressure in the line.

14. A system for controlling pressure in a line supplied from a blower comprising signal generating means including a device responsive to the pressure in the line operable to generate a signal in the form of pressure, the signal increasing in value with rise in pressure in the line and decreasing in value with a drop in pressure in the line, means governing the operation of the blower, means controlling said blower governing means comprising a regulator having a pressure responsive device responsive to the pressure of the signal, a device responsive to the flow of air through the blower acting in opposition to said last named pressure responsive device and means biasing said regulator to respond only to signal pressures above a certain value which value maintains a certain minimum of the blower, a by-pass connected to the line including a valve normally biased to open position, and a pressure responsive device responsive to the signal pressure and operable so long as critical volume. means responsive to the control signal and to the rate of operation of the blower to actuate said blower governing means, said con- .trol signal maintaining operation of the blowerabove the critical volume at all times, auxiliarymeans exercising control over the pressure in the line, and governing means for said auxiliary means responsive only to the control signal and only when the signal calls for a reduction in the volume of discharge below the critical volume.

HERBERT ZIEBOLZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 7 1,154,959 Banner Sept. 28, 1915 1,280,811 Moss Oct. 8, 1918 1,280,843 Rice Oct. 8, 1918 

